The present invention relates to a highly pure monoalkylphosphine and a method for preparing the same. The highly pure monoalkylphosphine is useful as a material for use in the epitaxial growth of compound semiconductors.
Recently, compound semiconductors have widely been used in various fields such as light emitting diodes, semiconductor lasers and high electron mobility transistors (HEMT). As a method for preparing a compound semiconductor, there has widely been used an epitaxial crystal-growth technique such as a Metalorganic Chemical Vapor Deposition (MOCVD) method. Compound semiconductors prepared by such an epitaxial crystal-growth technique include, for instance, Group III-V compound semiconductors in which phosphine containing a phosphorus atom is often used as a source for phosphorus atom, a Group V element.
Phosphines are highly toxic and suffer from a problem of safety. Recently, there has been proposed the use of monoalkylphosphorous atom-containing compounds as sources of phosphorus atom, one of group V elements, and they have attracted special interest recently as a substitute for phosphine since the use thereof permits the formation of epitaxial growth films having a low carbon content as an impurity and they are less toxic than phosphine.
As methods for preparing monoalkylphosphines, there have been known, for instance, those comprising reducing phosphonium chloride or phosphorous acid (see, for instance, Z. anorg. allg. Chem., 1978, 443, p. 42). However, these methods never permit the preparation of a highly pure monoalkylphosphines since they employ metallic catalysts in the reduction and suffer from a problem of contamination with metal impurities. Moreover, they include a production process requiring a long time period which results in a decrease of the yield of a desired product and makes the practice thereof in an industrial scale unfavorable. In addition, J. Org. Chem., 1959, 24, p. 356 discloses another method for preparing a monoalkylphosphine, which comprises reacting phosphine with an olefin. This method makes the mass production of monoalklphosphines substantially easier. However, this method includes a reaction in an aqueous system since it requires the use of an aqueous solution of an alkanesulfonic acid as a catalyst and accordingly, the method is liable to cause the formation of secondary and tertiary phosphine compounds as by-products whose removal is quite difficult and which inevitably lead to a decrease in the yield of the desired product.
Moreover, if impurities originated from the catalyst used are present in the resulting alkylphosphine, the compound semiconductor formed from a crystal prepared through the epitaxial growth of the phosphine does not exhibit desired electrical and optical properties at all. For this reason, an alkylphosphine for use in the production of a compound semiconductor is in general purified by high precision distillation. However, such high precision distillation in itself has not yet permitted the preparation of any monoalkylphosphine having a purity required for the production of a compound semiconductor.